Method of drying materials



Aug. 9, 1932. R. H. HoBRocK 1,871,269

METHOD 0F DRYING MATERIALSl Filed sept. 25, 1929 II [uuu lua Patented Aug. 9, 1932 method offdrying UNITED i STATES PATENT OFFICE,

BAYMON D H. HOBROCK, OF CHICAGO, ILLINOIS, ASSIGNOR TO WESTERN ELEOTRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD OF DRYING MATERIALS Application led September 25, 1929. Serial No. 395,108.

This invention relates to a method of drying materials, and more particularly to a materials having a normal moisture content. 'l

One of the most serious diiculties encountered in the manufacture of certain types of electrical condensers results from the reluctance which small vestiges of moisture,

remaining in paper employed as a dielectric in thecondensers, exhibit under attempts to remove them.

An object of the invention is to provide a simple method fordrying material, and one which will be of uniform and maximum eiliciency.

A preferred embodiment vofthe invention contemplates the application, through the paper dielectric, of a high potential, which due to the pronounced polarity existing in all water molecules and the relation ofspecilic inductive capacity and charge existing between the water and the walls of the capillary openings drives the minute particles of moisture contained in the capillaries of the paper Itlo the surface, whence it is revaporated'by eat.

The invention will be more fully understood from the following detailed description, reference being made to the accompanyling drawing forming a part thereof, in

which Fig. 1 is an enlarged fragmentary transverse sectional view of a condenser, shown composed of wound paper and tin foil, arranged in alternate layers;` w u Fig. 2 is a further enlarged fragmentary section taken on the line 2 2 of Fig. 1, showing the condition of a capillary after an initial heat treatment;

Fig. 3 is a viewfcorresponding to'Fig. 2, showing the condition ofthe capillary during a second heat treatment and beforea potential is applied across thedielectric; f

Fig. 4 Vis a'view corresponding to Fig. 3 showing the condition of the lcapillaries after thepotential has been applied; and

Fig. 5 is a diagrammatic view of an electric circuit employed `in the process. Y

Referring to the drawing, in which similar parts are' indicated by identical reference numerals, a condenser 10 includes a lead 11 preferably composed of thin sheet metal such as tin, copper or other suitable electrical con- A ducting material. The lead 11 has secured thereto at one end thereof one end of a sheet of tin foil 12, which inturn is engaged by one end of la sheet of paper 14. The condenser 10 also includes a second lead 15, similar to the lead 11, spaced therefrom and having secured to one end thereof one end of agn second tin foil sheet-16 which is engaged b one end of a second sheet of paper 17. t will be understood that the sheets of tin foil and paper may be, asin ordinary practice, several feet in length, dependent upon the capacity which it 1s desired that the condenser possess. In formin the condenser, leads 11 and 15 are held in teir spaced relation by any suitable means (not shown).

while the tin foil and paper sheets from each im -of the leads 11 and 15 are wrapped therearound continuously untilf'a compact roll is produced, comprising the condenser 10 shown in Fig. 1, wherein the foil comprising the elec` trodes and the paper sheets comprising the (7.5 dielectric are in alternate relation throughout the thickness of the condenser, and the leads 11l and 15 project a considerable vdistance bee` yond one edge of the condenser in the conventional manner (not shown).

Although the sheets 14 and 17 of the dielectric are usually of a type especially selected for use in condensers, they are, .like y ordinary paper, readil absorbent of moisture from the atmosp ere, being `n lade up essentially of cellulose particles jolned together in `a matrix with many very small Ipockets or capillary openings intrlcately interlaced throughout. For convenience, only one typical capillary 19 has `been shown in the drawing. lThe absorbed moisture may be held in the' capillary openings 19, as wa ter 20, (Fig, 2) and onsurfaces. of the-par'- ticles themselvesperhaps in some cases, small amounts of the remaining salts also re tain a share of the moisture and complicate the conductance phenomena produced under service conditions. Some of these salts ionize greatly decreasing the resistance of the dielectric 'and under proper conditions of moisture contained therein. Since some of this moisture is contained as highly dispersed water in the recesses of the capillaries 19 of the dielectric, it is extremely diiiicult to ,remove it therefrom by ordinary methods of evaporation. However, the importance of` removing it, and the results in the way of greatly increased resistance in the dielectric to be secured by its removal, are indicated by the fact that the average resistance of many typical condensers produced heretofore has been several thousand megohms less than the probable specific resistance of thoroughly dry pa er dielectric.

`This desire total drying of the dielectric may be accomplished by subjecting the dielectric to a series of three steps of treatment. Since the inal step of the series will be shown hereinafter to be all-effective and conclusive, under certain conditions the two reliminary steps may be dispensed with.

" owever, since under ordinary conditions the use of all three steps affords a substantial economy of time and expense, it is prefall be employed substantially as descri ed herein.

The following description will inform as to how the invention may be practiced; however, it should be understood that it ispurely illustrative in purpose and is not intended 4to limit the invention to the s eciic matter disclosed therein. In a specific instance, a number of wound condensers were placed in an air-tlght oven under an absolute pressure of about 5 millimeters of mercury, and subjected to a temperature of 120o centigrade for 2 hours. This resulted in the evaporation of a large portion of the free or surface moisture from the dielectric, giving the condition indicated in Fig. 2, wherein it will be observed that the only free moisture remaining is contained in the mouth of the capillary 19. Subsequently, Va current of dry air was permittedto iiow through the oven and about the condensers, and the temperature of the interior of the oven maintained at approximately 120 centigrade, for approximately 2 hours. At the expiration of such period all 'of the moisture wasevaporated from the surfaces of the dielectric and a portion of the water 20 from the mouth of the capillary openings, and a condition correonding to that indicated in Fig. 3,was proyuced, wherein it will be noticed that the only water remaining is contained in the 1'@- cesses of the capillary as residual moisture.

The combined effect of thetwo heat treatments just described was to reduce the moisture content of the dielectric to less than one percent of its original value; but even-that small amount if allowed to remain might contribute greatly to the early breakdown of the dielectric and other undesirable properties thereof, and must be removedin order qua ity.

These condensers were tested immediately upon completion of these two steps and were found to possess an average resistance value of approximately 1800 megohms, but this condition will obtain for only a short while, because the application of a high potential across the dielectric, aswhen the condenser is in service, will cause a gradual readjustment of the moisture in the capillaries and themigration of some of the water molecules outwardly to the openings of the capillaries, Where they will soon contact with the electrodes and eatly reduce the resistance of the dielectrlc by re-establishing conductance paths therethrough.

The third step ofthe process wasl carried out by connecting a group of nine condensers 10, 10 (Fig. 5) arranged in parallel with i each other, to a generator or other suitable source of unidirectional current 2l. A circuit for supplying the unidirectional currentto the group of condensers l0, 10ineluded a conductor 23 extending from a switch 24 to the source 21. The switch 24 was connected to the conductor 23 for the purpose of opening and closing the circuit at will. A second conductor 25 connected the condensers 10 to the switch4 24, and a milliammeter 26 was connected in turn to the condensers by a conductor 27. The circuit-also included a field rheostat or other voltage aduster 30 which was connected to the miliammeter 26 by a conductor 31, and a voltmeter 32 connected across the conductors 23 and 31.

In practice, the field rheostat 30 was adjusted to give a proper voltage and this voltage was applied across the dielectrics of the condensers by the closing of the switch v24. When the voltage was applied a current iiowed through the dielectric and was measured -by the milliammeter 26. Due to the electric charges andspecific inductive capacities of both the water, and the walls of the capillary, the water 2O moved in the capillary 19 in a definite direction. This movement of the water, which exemplified the well known phenomena of electroendosmosis, caused the water to collect in particles or globules at the surface of the dielectric or in the mouth of thel capillary, and the condition indica-ted in Fig. 4 was produced, wherein it will. be noted the residual water to 'lproduce a dielectric of extraordinary seenI t 120 milliamperes, was reached at the first 20 has been entirely expelled from the recesses of the capillary.

It will be understood that the operations just described took place while the condensers were in the atmosphere used in the second heating step. Consequently, as the moisture reached the surface of the dielectric, it was vaporized by contact with the adjacent hot tin foil electrodes or evaporated into the current of dry air. After the expiration of fifteen minutes from the time of application of the initial voltage and at recurrent intervals of fifteen minutes, the voltage was successively increased by volts until at the end of three hours-the expulsion of the final vestiges of water from the smallest and most remote capillaries was accomplished under an ap lied potential of approximately 450 volts.

ince the application of too much current is apt to cause a breakdown of the dielectric, the milliammeter 26 was provided for. the guidance of the operator. Although in the early stages of this third step of the rocess it is possible that the current might ecome excessive,'the relative values of the potential and the resistances of the dielectric used in the condensers employed in the experiment were such as to prevent the development of too much current. For instance, in the arrangement shown in Fig. 5 of the drawing,

when the nine condensers were connected in parallel and subjected to the initial potential, the current in the first instance was found to be 120 milliamperes, an his dropped sharpl to 20 iiiilliamperes, in short time. From t ence throu h the series of additional increases of vo tages the current valuevaried slightly, with however a pronounced downward trend until, upon the expiration of three hours and under an applied potential of 450 volts, the current value was approxi.

matel 1/40 milliamperes. It will thus be liat the greatest current value, namely stage or concurrent with the application of the voltage; however, this amount of current is not excessive for the paper dielectrics employed, since `they to it without deleterious eects.

Since the different dielectric materials and A the different grades of the same material are known to poss electrical chara eristics, a'nd since the current which will iow through tjie dielectric under agiven impressed voltage willvvary with theL specific resistance of the particular i grade of material used, and with other related electrical characteristics thereof, it is diicult, f

if not impossible, to determine that maxi- 'mumfcurrent value which may safely be per Y mitted to flow through a particular t' dielectric without causing dielectric reakdown, without experimenting with each type of dielectric employed. For the lsame reason,-

although it has been necessary above to deswere subjected more or less widely varying used pertain necessarily only to the specifictype of dielectric used, and obviously may vary in a degree to be determined by experiment where other materials are concerned.

The invention is obviously capable of successful application lto other types of paper and to all materials such as absorb or retain moisture in their capillaries. It is to be understood therefore that the invention should be limited only by the scope of the appended claims.

What is claimed is: 1

1. A method of treating a condenser which consists of evaporating the free moisture from the dielectric thereof and expelling the residual moisture from the dielectric by electroendosmosis.

from the dielectric thereof, expelling the residual moisture from the dielectric by electroendosmosis and evaporaing the expelled moisture. y 1 y 3. A method of treating a condenser which .consists of subjecting the dielectric-material of the condenser to heat to remove the free moisture therefrom and then .removing the residual moisture by applying a direct current potential across the dielectric material to Iproduce electroendosmosis therein.

4. The method of manufacturing electro-- static condenserscomposed of paper and metallic foils formed in a roll, which consists in subjecting the condenser to a preliminary drying process and thereafter connecting the metal foils with a source of direct c urrent potential to produce electroendosmosis in the aper and remove the residual moisture thererom.

5. A method of manlacturing electrostatic condensers compose of paper and metallic foils formed in a roll, which consists in subjecting said condenser to a preliminary drying process, and t ereafter connecting said metal foils with a sourcebf current, the potential of which is successively increased to produce electroendosmosis in the paper and remove residual moisture from the pa r.

In witness whereof,.I hereunto su scribe my nam'e this 14 day of September A. D., 1929.

RAYMOND H. HOBROCK. 

